Technical Field
The present invention relates to a circulating-current reducing circuit that reduces circulating current occurring in a transformer device, and a transformer unit including a transformer device having this circulating-current reducing circuit therein.
Related Art
Currently, various types of circuits provided with a transformer device are used in various applications, and there are many circuits having plural transformer devices connected therein. Not all of these transformer devices, which are included in these circuits, have the same specifications, and some have different specifications. It should be noted that the specifications of a transformer device as used herein mean parameters related to functions of the transformer device such as the number of turns in a coil or inductance of a coil of the transformer device.
The electric current supplied to the coil on the primary side of the transformer device is switched between ON and OFF at a certain frequency. At the time of switching of current from ON to OFF, circulating current flows from the higher impedance side to the lower impedance side in a closed loop formed on the primary side of plural transformer devices connected in parallel. The occurrence of circulating current causes ringing (abnormal) of current flowing in the circuit, which may cause a damage to elements in the circuit depending on the magnitude thereof.
For example, there is a switching power-source device described in Japanese Patent Application Laid-open No. H7-284271 as a known circuit for preventing the occurrence of circulating current. In the switching power-source device described in JP-H7-284271, plural switches are connected to the primary coils of the first transformer device and the second transformer device, and a capacitor is connected to each of the primary coil and the secondary coil. In addition, the switching power-source device described in JP-H7-284271 is provided with a control circuit that transmits signals to the plural switches to control them. The control circuit controls each of the switches so as to close or open in accordance with ON and OFF of the switching element, thereby controlling circulating current flowing between the primary coil of the first transformer and the primary coil of the second transformer.
However, the switching power-source device described above requires a control circuit that controls plural switches, which results in a disadvantage in terms of simplification and size-reduction of the entire device. In addition, if a high-functionality control circuit is used in such a switching power-source device to enhance the accuracy of control of the switches, this makes the device complicated, and may lead to an increase in cost thereof.
The present invention has been made in view of the fact described above, and relates to a circulating-current reducing circuit that, even with a simplified configuration having no control circuit used therein, can suppress the circulating current flowing between the primary coil of the first transformer device and the primary coil of the second transformer device, and also relates to a transformer unit including this circulating-current reducing circuit.